Utility Planet is the official blog for the column of the same name in The Spectrum Monitor. It replaces Utility World in the discontinued Monitoring Times magazine. Utilities are all VLF/LF/MF/HF (and sometimes low-band VHF) radio communications except broadcasting, CB, and non-emergency amateur. If you understood the last sentence, you know enough to read this blog.

Tuesday, October 25, 2011

After a long interval with no changes, Aeronautical Radio, Inc (ARINC) has revised the system table used in its High-Frequency Data Link (HFDL) network.

Two updates, numbers 42 and 43, were issued in the space of about one day. Number 43 (2B in hex) is still current at this time.

The system table is a lookup database of all frequencies used by HFDL stations. For our use, it is essential in order to change the numbers passed in HFDL "squitters" to the frequencies in use at a given time. One can look this up manually on a text file or spreadsheet of the system table, but it is far quicker to configure software to do it automatically.

In the case of the most popular program, PC-HFDL, this can be done in two ways. The first is to get lucky, and have PC-HFDL open when the system passes the new frequencies to aircraft. This works for the first few days after a change, before the information finally propagates to all users.

The second, and most practical, procedure is to replace the old pchfdl.dat file in the program's runtime directory. This is done by obtaining the new file from someone who has made the update, usually from web sites or links posted to mailing lists. Then close PC-HFDL if it's open. Find the right directory, rename the existing file to oldpchfdl.dat, and copy in the new one as pchfdl.dat. Then restart PC-HFDL and see if the numbers have changed back to freqs.

The structure of pchfdl.dat is completely bizarre, containing incomprehensible snippets of HFDL decodes. However, it works - most of the time.

The new file will be added to this column's web site as soon as I can obtain and test it. This will probably happen around Thursday. Tomorrow, I'll be on an airplane myself.